The invention relates to a triaxial focal plane shutter, and more particularly, to a triaxial focal plane shutter utilizing cloth blinds in which first blind winding pulleys and a second blind winding drum are disposed in substantially coaxial manner.
As is known, triaxial focal plane shutters utilizing cloth blinds have been used extensively in single lens reflex cameras in the past. However, at the present time, the general trend is directed toward the use of four axis focal plane shutters utilizing cloth blinds, and only a very few cameras utilize a triaxial arrangement. This is because of the specific construction of conventional triaxial focal plane shutter in which a first blind winding pulley and a second blind winding drum are coaxially disposed on a single support shaft so as to be independently rotatable and in which during a shutter winding operation, they are rotated substantially integrally, which resulted in a complex and bulky arrangement for the support mechanism and the coupling mechanism associated with the first blind winding pulley and the second blind winding drum. Because of the complexity of the coupling mechanism, it is difficult to provide a bearing mounted on a stationary member which provides an independent support for the second blind winding drum. Rather, the drum must be indirectly mounted on a first blind winding shaft on which the first blind winding pulley is mounted. As a result, to form the coupling mechanism, a number of gears and clutches must be disposed around the first blind winding pulley and the second blind winding drum which are disposed in coaxial manner. This results in an increased size of the focal plane shutter itself, and the complex coupling mechanism is likely to cause a failure. The failure is particularly likely when either the first or the second blind is stopped in the course of its running.
A gear contained in the coupling mechanism which couples the first blind winding pulley and the second blind winding drum is partly maintained in coupled relationship with the first blind winding pulley and the second blind winding drum and also rotates together as the first and the second blind run, with the result that the inertia of the gear causes a failure to produce a stabilized running speed of the blind.
A lack of stability in the running speed of the blind during the operation of the conventional triaxial focal plane shutter is also caused by the inertia of transmission gears or rollers connected to a film winding mechanism or a shutter speed presetting dial and which are also operated at the same time as the first blind winding pulley or the second blind winding drum.